1. Field of the Invention
The invention relates generally to resistive chip devices for electronic systems. In particular, the invention relates to a resistor device that provides only a minimal variation in resistance over an operating temperature range.
2. Description of the Related Art
A resistor is designed to produce a voltage across its terminals proportional to the electric current that passes through it. Resistors are used in nearly every kind of electronic equipment available today. For many types of resistive materials, their resistivity can change significantly as the ambient temperature changes. When such variations occur, electrical equipment in which the resistive device is employed may not perform as accurately as necessary, or may fail entirely. It has also been found in working with composite resistor films, that the properties of such films change after they are temperature treated or annealed. This change is not always predictable because of variations in the resistive material on a microscopic scale, caused by an interdiffusion of the two materials during high-temperature treatments that can affect the sheet resistance and the temperature coefficient of resistance of the resistive thin film material. Known devices designed to counteract this effect have disadvantages. They are typically made from cermet alloys or metallic alloy foils. Cermet alloys cannot achieve precisely controlled temperature coefficient of resistance values. Metallic alloy foils, on the other hand, cannot achieve high resistance values.
It would be desirable to have a resistor device that has both precise temperature coefficients of resistance and is able to achieve high resistance values. Such a device would allow electronic devices to operate without significant effect from changes in ambient temperature conditions and would allow the devices to be more reliable and precise in use.